Significantly raising tetracyanoquinodimethane electrode performance in zinc-ion battery at low temperatures by eliminating impurities

Applications of organic compounds-based electrodes in aqueous zinc-ion batteries (AZIBs) at low temperatures are severely restricted by the freezing of aqueous electrolytes and the inferior dynamic behavior of organic electrodes below zero. Herein, tetracyanoquinodimethane (TCNQ) was purified by the sublimation method and used as a cathode in AZIBs to investigate electrochemical Zn storage performance in comparison with nonpurified TCNQ at a temperature range of 25 degrees C to -40 degrees C. Nuclear magnetic resonance and elemental analysis prove increased purity in purified TCNQ (p-TCNQ), whereas scanning electron microscope and Brunner-Emmet-Teller data verify reduced particle size and increased surface area of p-TCNQ. Kinetic analysis demonstrates that p-TCNQ is a more surface-controlled electrode process than TCNQ and offers much higher ionic diffusivity than the latter at various temperatures. Molecular dynamics simulation validates that the existence of impurity increases the absorption energy of TCNQ in a TCNQ//Zn system that is unfavorable to Zn migration. Comprehensive analysis, including ex situ X-ray diffraction, Fourier transform infrared, Raman, and electron spin-resonance spectroscopy characterization confirm the high reversibility of transformation between C N and -C=N groups in p-TCNQ. This work provides a simple, environmentally friendly strategy to fabricate a high-performance AZIB at low temperatures while offering fundamental chemistry insight into organic electrode performance, thus possessing universal significance.